ABSTRACT
The idea of vegetation (or ecological) succession has proved hugely important in ecology. Henry Chandler Cowles (1899) proposed a formal concept of succession based on the vegetation of sand dunes (the Indiana Dunes) on the shores of Lake Michigan, USA. Frederic Edward Clements (1916) developed the idea of succession, which he saw as a predetermined sequence of developmental stages, or sere, that ultimately leads to a self-perpetuating, stable community called climatic climax vegetation that then endures. He recognized six stages in any successional sequence: (1) nudation – an area is left bare after a major disturbance; (2) migration – species arrive as seeds, spores, and so on; (3) ecesis – the plant seeds establish themselves; (4) competition – the established plants complete with one another for resources; (5) reaction – the established plants alter their environment and so enable other new species to arrive and establish themselves; (6) stabilization – after several waves of colonization, an enduring equilibrium is achieved. Clements distinguished between primary succession and secondary succession. Primary succession occurs on newly uncovered bare ground that has not supported vegetation before. New oceanic islands, ablation zones in front of glaciers, developing sand dunes, fresh river alluvium, newly exposed rock produced by faulting or volcanic activity, and such human-made features as spoil heaps are all open to first-time colonization. The full sequence of successional communities forms a primary sere (prisere), with different priseres occurring on different substrates: hydrosere in open water (where succession could lead to woodland); haloseres in salt marshes; psammosere on sand dunes; and lithoseres on bare rock. Secondary succession occurs on severely disturbed ground that previously supported vegetation. Fire, flood, forest clearance, the removal of grazing animals, hurricanes, and many other factors may inaugurate secondary succession.
